class 9 biology chapter 7 enzymes mcqs

Class 9 – Chapter 7: Enzymes | MCQs (1–20)

Section 1: Basic Concepts of Enzymes

1. Enzymes are
   a) Proteins
   b) Carbohydrates
   c) Fats
   d) Vitamins
   ✅ Answer: a) Proteins

2. Enzymes are produced by:
   a) Ribosomes
   b) Mitochondria
   c) Chloroplast
   d) Nucleus
   ✅ Answer: a) Ribosomes

3. The function of enzymes is to
   a) Destroy cells
   b) Slow down reactions
   c) Speed up reactions
   d) None of these
   ✅ Answer: c) Speed up reactions

4. The substance on which an enzyme acts is called:
   a) Substrate
   b) Inhibitor
   c) Catalyst
   d) Product
   ✅ Answer: a) Substrate

5. The part of the enzyme where the substrate binds is
   a) Nucleus
   b) Active site
   c) Passive site
   d) Vacuole
   ✅ Answer: b) Active site

6. Enzymes are made up of:
   a) DNA
   b) Lipids
   c) Proteins
   d) RNA
   ✅ Answer: c) Proteins

7. Enzymes act as
   a) Inhibitors
   b) Catalysts
   c) Products
   d) Reactants
   ✅ Answer: b) Catalysts

8. Which of the following affects enzyme activity?
   a) Light
   b) Sound
   c) Temperature
   d) Electricity
   ✅ Answer: c) Temperature

9. Enzyme activity is maximum at:
   a) Low temperature
   b) Optimum temperature
   c) Freezing point
   d) High pressure
   ✅ Answer: b) Optimum temperature

10. Enzymes are denatured at
    a) Low temperature
    b) High pressure
    c) High temperature
    d) Moderate temperature
    ✅ Answer: c) High temperature

11. Enzymes work by:
    a) Raising activation energy
    b) Lowering activation energy
    c) Blocking reactions
    d) Breaking down DNA
    ✅ Answer: b) Lowering activation energy

12. All enzymes are:
    a) Lipids
    b) Vitamins
    c) Proteins
    d) Sugars
    ✅ Answer: c) Proteins

13. Enzymes are specific in:
    a) Location
    b) Substrate
    c) Size
    d) Shape only
    ✅ Answer: b) Substrate

14. The enzyme that breaks down starch is
    a) Protease
    b) Lipase
    c) Amylase
    d) Lactase
    ✅ Answer: c) Amylase

15. Enzymes are needed in:
    a) Small amounts
    b) Large amounts
    c) Unlimited quantity
    d) Daily
    ✅ Answer: a) Small amounts

16. Which of these is a digestive enzyme?
    a) Trypsin
    b) Hemoglobin
    c) Insulin
    d) Keratin
    ✅ Answer: a) Trypsin

17. Which of the following is not a characteristic of enzymes?
    a) Reusable
    b) Specific
    c) Used up in reaction
    d) Protein in nature
    ✅ Answer: c) Used up in reaction

18. Which organ produces most digestive enzymes?
    a) Brain
    b) Pancreas
    c) Heart
    d) Kidney
    ✅ Answer: b) Pancreas

19. Which factor does not affect enzyme action?
    a) Temperature
    b) pH
    c) Light
    d) Substrate concentration
    ✅ Answer: c) Light

20. The enzyme lipase breaks down:
    a) Proteins
    b) Carbohydrates
    c) Nucleic acids
    d) Fats
    ✅ Answer: d) Fats

Section 2: Structure & Mechanism of Enzyme Action

21. The place where an enzyme binds to its substrate is called the:
    a) Core
    b) Active site
    c) Binding cell
    d) Reaction zone
    ✅ Answer: b) Active site

22. The model describing enzyme-substrate interaction is
    a) Passive model
    b) Lock and key model
    c) Puzzle model
    d) Binding theory
    ✅ Answer: b) Lock and key model

23. Enzymes reduce the ___________ energy needed for a reaction.
    a) Binding
    b) Kinetic
    c) Activation
    d) Heat
    ✅ Answer: c) Activation

24. Which bond helps maintain the structure of enzymes?
    a) Covalent bonds only
    b) Ionic bonds only
    c) Hydrogen bonds
    d) Only peptide bonds
    ✅ Answer: c) Hydrogen bonds

25. Which structural level of a protein is responsible for enzyme activity?
    a) Primary
    b) Secondary
    c) Tertiary
    d) Quaternary
    ✅ Answer: c) Tertiary

26. An enzyme-substrate complex is:
    a) A permanent bond
    b) Temporary structure during a reaction
    c) A type of sugar
    d) An enzyme inhibitor
    ✅ Answer: b) Temporary structure during a reaction

27. The enzyme-substrate complex is formed at the:
    a) Cytoplasm
    b) Active site
    c) Mitochondria
    d) Ribosome
    ✅ Answer: b) Active site

28. After a reaction, the enzyme:
    a) Is destroyed
    b) Becomes part of the product
    c) Detaches unchanged
    d) Changes shape permanently
    ✅ Answer: c) Detaches unchanged

29. The specificity of enzymes depends on
    a) The number of substrates
    b) The shape of the active site
    c) The pH of solution
    d) The number of products
    ✅ Answer: b) The shape of the active site

30. The lock and key model was proposed by
    a) Watson
    b) Fischer
    c) Mendel
    d) Darwin
    ✅ Answer: b) Fischer

31. An enzyme can act
    a) Only once
    b) Multiple times
    c) Only on one type of reaction
    d) Only when heated
    ✅ Answer: b) Multiple times

32. In enzyme activity, what is released after the reaction?
    a) Substrate
    b) Product
    c) Enzyme
    d) Heat
    ✅ Answer: b) Product

33. Which part of the enzyme changes shape in the induced fit model?
    a) Substrate
    b) Active site
    c) Product
    d) Whole enzyme
    ✅ Answer: b) Active site

34. The term "enzyme-substrate complex" means:
    a) Enzyme and product
    b) Substrate and product
    c) Enzyme bonded to substrate temporarily
    d) Enzyme permanently destroyed
    ✅ Answer: c) Enzyme bonded to substrate temporarily

35. A coenzyme is
    a) A protein
    b) A mineral
    c) An organic helper molecule
    d) A DNA segment
    ✅ Answer: c) An organic helper molecule

36. Cofactors that help enzymes can be
    a) Vitamins
    b) Minerals
    c) Both a and b
    d) None of these
    ✅ Answer: c) Both a and b

37. If the active site is altered, the enzyme becomes:
    a) Faster
    b) Inactive
    c) Stronger
    d) More efficient
    ✅ Answer: b) Inactive

38. The induced fit model suggests that:
    a) Enzyme remains rigid
    b) Substrate forces the enzyme to fit
    c) Enzyme molds around the substrate
    d) Active site never changes
    ✅ Answer: c) Enzyme molds around the substrate

39. Which condition can cause an enzyme’s active site to change shape?
    a) Constant pH
    b) Low substrate concentration
    c) High temperature
    d) Regular body temperature
    ✅ Answer: c) High temperature

40. The catalytic activity of enzymes is dependent on:
    a) Their color
    b) Their 3D shape
    c) Their DNA
    d) Their weight
    ✅ Answer: b) Their 3D shape

Section 3: Types and Examples of Enzymes

41. Enzymes that break down proteins are called:
    a) Amylases
    b) Proteases
    c) Lipases
    d) Lactases
    ✅ Answer: b) Proteases

42. The enzyme that digests starch is
    a) Pepsin
    b) Amylase
    c) Lipase
    d) Trypsin
    ✅ Answer: b) Amylase

43. Lipase acts on:
    a) Proteins
    b) Sugars
    c) Fats
    d) DNA
    ✅ Answer: c) Fats

44. Which enzyme is found in saliva?
    a) Pepsin
    b) Lipase
    c) Salivary amylase
    d) Lactase
    ✅ Answer: c) Salivary amylase

45. Pepsin works in the:
    a) Mouth
    b) Small intestine
    c) Stomach
    d) Liver
    ✅ Answer: c) Stomach

46. Trypsin works best in:
    a) Acidic pH
    b) Basic pH
    c) Neutral pH
    d) Salty solutions
    ✅ Answer: b) Basic pH

47. Lactase is an enzyme that breaks down
    a) Sucrose
    b) Starch
    c) Lactose
    d) Fructose
    ✅ Answer: c) Lactose

48. Which enzyme breaks down hydrogen peroxide into water and oxygen?
    a) Catalase
    b) Oxidase
    c) Protease
    d) Lipase
    ✅ Answer: a) Catalase

49. Which enzyme breaks down DNA?
    a) Nuclease
    b) Amylase
    c) Protease
    d) Lipase
    ✅ Answer: a) Nuclease

50. Which enzyme is used in the dairy industry to make cheese?
    a) Pepsin
    b) Chymosin
    c) Trypsin
    d) Amylase
    ✅ Answer: b) Chymosin

51. The enzyme used in detergents to break down stains is
    a) Amylase
    b) Protease
    c) Lipase
    d) All of these
    ✅ Answer: d) All of these

52. Enzymes are named by adding which suffix?
    a) -ose
    b) -ase
    c) -ite
    d) -zyme
    ✅ Answer: b) -ase

53. Which of the following is not an enzyme?
    a) Maltase
    b) Glucose
    c) Lipase
    d) Lactase
    ✅ Answer: b) Glucose

54. Rennin is an enzyme found in:
    a) Plants
    b) Infants’ stomachs
    c) Blood
    d) Liver
    ✅ Answer: b) Infants’ stomachs

55. Which of the following breaks down sucrose?
    a) Amylase
    b) Invertase
    c) Lipase
    d) Protease
    ✅ Answer: b) Invertase

56. An enzyme that joins molecules together is called:
    a) Synthase
    b) Ligase
    c) Polymerase
    d) All of these
    ✅ Answer: d) All of these

57. An enzyme that cuts DNA at specific sites is
    a) Restriction enzyme
    b) Helicase
    c) Polymerase
    d) Ligase
    ✅ Answer: a) Restriction enzyme

58. Enzymes responsible for removing phosphate groups are called:
    a) Kinases
    b) Phosphatases
    c) Lipases
    d) Amylases
    ✅ Answer: b) Phosphatases

59. DNA polymerase is responsible for:
    a) Breaking DNA
    b) Synthesizing DNA
    c) Destroying DNA
    d) Repairing RNA
    ✅ Answer: b) Synthesizing DNA

60. Which of the following enzymes is found in the liver and breaks down toxins?
    a) Catalase
    b) Pepsin
    c) Trypsin
    d) Sucrase
    ✅ Answer: a) Catalase

Section 4: Factors Affecting Enzyme Activity

61. Which of the following can increase enzyme activity up to a limit?
    a) Extremely high temperature
    b) Moderate increase in temperature
    c) Freezing
    d) Boiling
    ✅ Answer: b) Moderate increase in temperature

62. Enzymes show maximum activity at:
    a) 0°C
    b) Room temperature
    c) Optimum temperature
    d) Any temperature
    ✅ Answer: c) Optimum temperature

63. Extremely high temperature causes enzymes to:
    a) Activate
    b) Multiply
    c) Denature
    d) Divide
    ✅ Answer: c) Denature

64. Denaturation of enzymes means:
    a) Increasing speed
    b) Permanent loss of function
    c) Reversible reaction
    d) Better efficiency
    ✅ Answer: b) Permanent loss of function

65. The pH value at which an enzyme works best is called:
    a) Normal pH
    b) Basic pH
    c) Optimum pH
    d) Extreme pH
    ✅ Answer: c) Optimum pH

66. Pepsin works best in:
    a) Neutral pH
    b) Alkaline pH
    c) Acidic pH
    d) Any pH
    ✅ Answer: c) Acidic pH

67. Trypsin works best at:
    a) pH 2
    b) pH 7
    c) pH 8
    d) pH 10
    ✅ Answer: c) pH 8

68. What happens to enzyme activity at very low temperatures?
    a) It increases
    b) It remains the same
    c) It slows down
    d) It denatures
    ✅ Answer: c) It slows down

69. The enzyme activity is affected by:
    a) pH
    b) Temperature
    c) Substrate concentration
    d) All of these
    ✅ Answer: d) All of these

70. Enzyme activity increases with increasing substrate concentration until:
    a) Substrate is used up
    b) All enzymes are occupied
    c) Reaction ends
    d) All of the above
    ✅ Answer: b) All enzymes are occupied

71. Too high or too low pH can:
    a) Improve enzyme structure
    b) Denature the enzyme
    c) Speed up all enzymes
    d) Have no effect
    ✅ Answer: b) Denature the enzyme

72. The effect of temperature on enzymes is:
    a) Linear
    b) Bell-shaped curve
    c) No effect
    d) Random
    ✅ Answer: b) Bell-shaped curve

73. A graph of enzyme activity vs. temperature shows:
    a) Constant rise
    b) Constant fall
    c) Rise and then sudden drop
    d) No change
    ✅ Answer: c) Rise and then sudden drop

74. Low temperature slows enzymes by reducing:
    a) Heat
    b) Kinetic energy of molecules
    c) Enzyme shape
    d) Binding
    ✅ Answer: b) Kinetic energy of molecules

75. Substrate concentration affects enzyme activity until:
    a) Product forms
    b) Enzyme becomes inactive
    c) All active sites are full
    d) No enzyme remains
    ✅ Answer: c) All active sites are full

76. A higher enzyme concentration usually:
    a) Decreases rate
    b) Increases rate
    c) Has no effect
    d) Denatures substrate
    ✅ Answer: b) Increases rate

77. Enzymes are sensitive to:
    a) Electric current
    b) Environmental conditions
    c) Magnetism
    d) Color
    ✅ Answer: b) Environmental conditions

78. Which factor is not known to affect enzyme activity?
    a) Temperature
    b) pH
    c) Substrate concentration
    d) Light color
    ✅ Answer: d) Light color

79. High substrate concentration results in:
    a) Slower reaction
    b) No enzyme activity
    c) Faster reaction until saturation
    d) Instant denaturation
    ✅ Answer: c) Faster reaction until saturation

80. After reaching saturation, adding more substrate:
    a) Speeds up the reaction
    b) Slows the reaction
    c) Has no effect
    d) Denatures the enzyme
    ✅ Answer: c) Has no effect

Section 5: Applications & Biological Importance of Enzymes

81. Enzymes are essential for:
    a) Breathing
    b) Digestion
    c) Circulation
    d) Filtration
    ✅ Answer: b) Digestion

82. Without enzymes, metabolic reactions would:
    a) Happen faster
    b) Not occur at all
    c) Occur too slowly to sustain life
    d) Produce more energy
    ✅ Answer: c) Occur too slowly to sustain life

83. Enzymes help in:
    a) Transporting oxygen
    b) Speeding up chemical reactions
    c) Carrying nutrients
    d) Breaking chromosomes
    ✅ Answer: b) Speeding up chemical reactions

84. In digestion, enzymes break large molecules into:
    a) Smaller molecules
    b) Ions
    c) Atoms
    d) Gases
    ✅ Answer: a) Smaller molecules

85. Which of the following industries use enzymes?
    a) Food
    b) Medicine
    c) Textile
    d) All of these
    ✅ Answer: d) All of these

86. Enzymes are used in the dairy industry to:
    a) Kill bacteria
    b) Increase milk production
    c) Make cheese and yogurt
    d) Cool the milk
    ✅ Answer: c) Make cheese and yogurt

87. Enzymes in washing powders break:
    a) Proteins and fats in stains
    b) Fibers
    c) Threads
    d) Buttons
    ✅ Answer: a) Proteins and fats in stains

88. Which enzyme is used in glucose testing strips?
    a) Lactase
    b) Glucose oxidase
    c) Amylase
    d) Lipase
    ✅ Answer: b) Glucose oxidase

89. Enzymes in biotechnology are used to:
    a) Slow down fermentation
    b) Stop DNA replication
    c) Cut and paste DNA
    d) Color cells
    ✅ Answer: c) Cut and paste DNA

90. Enzymes used in genetic engineering are called:
    a) Synthase
    b) Ligase and Restriction enzymes
    c) Oxidase
    d) Protease
    ✅ Answer: b) Ligase and Restriction enzymes

91. Enzymes used to manufacture biofuels are involved in breaking:
    a) Metals
    b) Carbohydrates
    c) Water
    d) DNA
    ✅ Answer: b) Carbohydrates

92. Amylase helps convert starch into:
    a) Lipids
    b) Glucose
    c) Fructose
    d) Protein
    ✅ Answer: b) Glucose

93. Enzymes used in tenderizing meat are:
    a) Proteases
    b) Amylases
    c) Nucleases
    d) Lipases
    ✅ Answer: a) Proteases

94. Which enzyme is used to soften fruits in the food industry?
    a) Pectinase
    b) Sucrase
    c) Lipase
    d) Protease
    ✅ Answer: a) Pectinase

95. Enzymes speed up reactions by:
    a) Increasing heat
    b) Adding pressure
    c) Lowering activation energy
    d) Removing water
    ✅ Answer: c) Lowering activation energy

96. Which property makes enzymes useful in industries?
    a) Flexibility
    b) Small size
    c) High specificity and efficiency
    d) Bright color
    ✅ Answer: c) High specificity and efficiency

97. Enzymes are reused because they are:
    a) Very expensive
    b) Not changed in the reaction
    c) Made of glucose
    d) Harmful if left
    ✅ Answer: b) Not changed in the reaction

98. Enzymes used in diagnostic kits help to:
    a) Kill viruses
    b) Detect chemical changes
    c) Generate heat
    d) Clean organs
    ✅ Answer: b) Detect chemical changes

99. Biological washing powders contain:
    a) Hormones
    b) Antibiotics
    c) Enzymes
    d) Acids
    ✅ Answer: c) Enzymes

100. Enzymes are essential for life because they:
     a) Give energy directly
     b) Are stored as fat
     c) Enable vital reactions to occur fast enough
     d) Absorb oxygen
     ✅ Answer: c) Enable vital reactions to occur fast enough